server: (UI) add syntax highlighting and latex math rendering (#10808)

server: (UI) add syntax highlighting and latex math rendering (#10808)

* add code highlighting and math formatting

* code cleanup

* build public/index.html

* rebuild public/index.html

* fixed coding style

* fixed coding style

* style fixes

* highlight: smaller bundle size, fix light & dark theme

* remove katex

* add bundle size check

* add more languages

* add php

* reuse some langs

* use gzip

* Revert "remove katex"

This reverts commit c0e5046accd10be3f83018cffdc29a652849fc61.

* use better maintained @vscode/markdown-it-katex

* fix gzip non deterministic

* ability to add a demo conversation for dev

* fix latex rendering

* add comment

* latex codeblock as code

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Co-authored-by: Xuan Son Nguyen <redacted>